The present invention is related to the field of sample identification, in particular to a method for identifying or discriminating biological species from non-biological species, whether they are individual particles or components of a composition. The invention lies in the field of pump-probe fluorescence spectroscopy for time-resolved imaging. It uses the differences in UV induced fluorescence of biological samples vs. non-biological samples when they are exposed to radiation, in particular the fact that the UV fluorescence of bio particles changes, in particular is depleted, by the addition of visible radiation, whereas the UV fluorescence of non-bio particles does not change, in particular is not depleted, under the same condition.
Similar effects were reported using quantum coherence effects in pump-probe femtosecond experiments as described e.g. in “Pump-Probe Depletion Spectroscopy Discriminates Organic and Biological Molecules” by F. Courvoisier, J.-P. Wolf et al. in App. Phys. Lett. 87(6) 063901 (2005) and some subsequent publications by the same group. These experiments use a femtosecond 266 nm pump laser and a femtosecond 800 nm probe pulse.
This coherent control experiment requires rather complex and expensive equipment and thus limits its use to laboratories or to experimental setups. A main disadvantage of prior art solutions and applications is the necessity to use lasers with extremely short pulse durations, usually in the femtosecond range. Such lasers are sensitive, usually rather expensive, unrugged instruments requiring precise adjustment and cautious handling. Also, they often produce non-linear perturbations and unwanted dispersion in attached fibers and probe media to be investigated, thus complicating measurements and leading to unexact results.
It would thus be advantageous if one could use compact, cost effective and rugged lasers producing longer pulses instead of such sensitive femtosecond devices.
On the other hand it was found that biological organic material like amino-acids or material containing aromatic amino-acids, like peptides, proteins, bacteria, viruses, pollens, spores, as well as other biological species like flavins or NAD/NADH (nicotinamide adenine dinucleotide, a coenzyme), exhibits fluorescence depletion in pump-probe arrangements longer than one picosecond, while non-biological organic material like aromatic (AH) or polyaromatic hydrocarbons (PAH) or containing such hydrocarbons, carbonaceous aerosols, or soot, do not exhibit such fluorescence depletion.
This finding allows to discriminate biological material or particles from non-biological particles by using the pump-probe method/arrangement with a laser producing longer pulses, here meaning pulses longer than one picosecond, preferably in the nanosecond range. Even the use of continuous wave (CW) lasers seems reasonable.
The optical identication of bioaerosols in the atmosphere and their discrimination against combustion related particles is a major issue for real-time, field-compatible instruments. The present invention aims at embedding advanced pump-probe depletion spectroscopy accordingly in such portable equipment.